1. Field of the Invention
The invention relates to a method for applying and removing elastic rail clips or fasteners and, more particularly, to a method for applying and removing rail clips or fasteners which are applied by movement transverse to the longitudinal centerline of the rail. The invention additionally relates to a method and apparatus for removing previously-applied rail clips.
2. Discussion of the Related Art
Elastic or spring clips or fasteners are used with increasing regularity to fasten rails to concrete or wooden ties. Some clips, such as the so-called "Pandrol e" clip, are applied by movement parallel with the longitudinal centerline of the rail. Others, such as the so-called "Safelok" clip, are applied by movement transverse to the longitudinal centerline of the rail. It is with the application and removal of transversely applied clips that the invention is concerned.
Safelok clips and other transversely applied clips are characterized by their insertion into and through a support shoulder imbedded or secured to a tie such that a toe or free end of the clip applies a holding force to the base of the rail either via direct contact with the rail or, in the case of concrete ties, via an intermediate insulator pad. The applied clips are held in position by latching contact with the sockets. Driving a clip into its rail tensioning position (generally known in the art as "applying" the clip) is a relatively difficult process because it requires the imposition of substantial forces to the base or heel of the clip in a direction transverse to the longitudinal centerline of the rail. Retracting or removing a previously applied clip for track maintenance or replacement is even more difficult because it requires the imposition of 1) transverse retraction forces of a magnitude comparable to the magnitude of the application forces required to apply the clip and 2) lateral compression forces of sufficient magnitude to squeeze the arms of the clip together to unlock the clip from the socket and to crush ballast lodged between the arms of the clip.
Previous attempts have been proposed to either apply or remove transversely applied clips. However, all such attempts exhibited some drawbacks and disadvantages, and no attempt has been made to provide a machine capable of automatically both applying and removing transversely applied clips.
Devices for applying transversely applied clips are disclosed in U.S. Pat. No. 4,494,463 to Young et al. (the Young patent), U.S. Pat. No. 5,165,346 to Piekarski (the Piekarski patent), and U.S. Pat. No. 5,269,225 to Bosshart et al. (the Bosshart patent). The Piekarski patent discloses a manually operated, lever actuated device having 1) a hook which hooks onto the head of the rail and 2) a pin which slips through the rail clip and which draws the clip towards the rail to apply the clip upon manual pivoting of the lever. This device is capable of applying only one clip at a time and, of course, cannot be operated automatically.
The Young patent and Bosshart patent each disclose a machine having pivot arms which each bear an applicator tool which engages the heel of a clip and drive the clip transversely towards the rail to apply the clip. Both patents disclose two pivot arms for each rail with each pivot arm receiving respective gauge and field side applicator tools. The pivot arms are operated simultaneously by a hydraulic cylinder to apply both field and gauge side clips simultaneously. While the clip applicator machines of the Young and Bosshart patents are capable of applying multiple clips simultaneously and of being operated automatically, they are not easily adapted to accommodate variations in rail configuration, rail orientation, or clip orientation. Moreover, the machines disclosed in the Bosshart and Young patents, like the device disclosed in the Piekarski patent, cannot remove previously applied clips.
U.S. Pat. No. 4,580,501 to Collins (the Collins patent) discloses a clip extractor mechanism for automatically removing or extracting previously applied clips. The clip extractor mechanism disclosed in the Collins patent includes a pair of opposed abutment plates which are of identical structure and which are mounted on a support so as to be pivotable about an axis perpendicular to the rail. Each abutment plate supports a pair of pivot arms that are pivotable about an axis extending in parallel with the rail. In operation, the clip extractor mechanism is initially brought into contact with the rail head, and the abutment plates are then pivoted longitudinally towards one another to engage the clip arms so as to laterally compress the clips and to prepare them for removal. Then, the pivot arms are pivoted outwardly transversely away from the rail to drive the clips away from the rail. Hence, field and gauge side clips are removed automatically by the same mechanism. However, this mechanism is relatively intolerant to imperfectly positioned or orientated rails and/or clips and is incapable of applying clips.